Electrical distribution system



7 Sheets-Sheet 1 2- I vJw.

g a {53a J. s. PARSONS ELECTRICAL DISTRIBUTION SYSTEM Original Filed June 28, 1940 Fiyrl.

Dec. 11, 1945.

INVENTOR John S.Parsons. AORNEY saw WITNESSES: 7

LTamwl 3 J. S. PARSONS ELECTRICAL DISTRIBUTION SYSTEM Dec. 11, 1945.

Original Filed June 28, 1940 7 Sheets-Sheet 2 ct- ,1 L J Peril INVENTOR- Jolm S Parsons.

WITNESSES:

I An RNEY Dec. 11, 1945. J. 5. PARSONS 2,390,810

ELECTRICAL DISTRIBUTION SYSTEM Original Filed June 28, 1940 '7 Sheets-Sheet 3 WITNESSES: W v John 5'. Parsons.

BY v INVENTOR Dec. 11, 1945. J. s. PARSONS 2,390,810

ELECTRICAL DISTRIBUTION SYSTEM Original File d June 28, 1940 7 Sheets-Sheet 4 1113 1 12 Eye)". I y I r 115 17 1'!) Fig. 6.

WITNESSES: INVENTOR John S. Parsons.

ATT

Dec. 11, 1945'. I J. 5. PARSONS ELECTRICAL DISTRIBUTION SYSTEM Original Filed June 28, 1940 '7 Sheets-Sheet 5 WITNESSES: I INVENTOR I W v John S- PUPS'OH-S.

Dec. 11, 1945. I J. 5. PARSONS 2,390,810

ELECTRICAL DISTRIBUTION SYSTEM Original Filed Juhe '28, 1940 7 Sheets-Sheet 6 2 25a w m b 6'? Q I: c

1 15 J 1347AA wmuzsszs; INVENTOR W John 3. Parsons.

. BY 7 I Arrkuav J. S. PARSONS ELECTRICAL DISTRIBUTION SYSTEM Original Filed June 28, 1940 7 Sheets-Sheet 7 & E S S E N H W INVENTOR' John S.Pars ons.

A RNEY Patented Dec. 11, 1945 ELECTRICAL DISTRIBUTION SYSTEM John S. Parsons, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Original application June 28, 1940, Serial No. 342,940, now Patent N 0. 2,329,132, dated August 7, 1943. Divided and this application April 29, 1942, Serial No. 440,960

9 Claims.

This invention relates to electrical distribution systems and it has particular relation to network distribution systems of the type wherein a plurality of primary feeder circuits are employed for supplying energy to a common secondary network or grid circuit.

This application is a division of application Serial No. 342,940, filed June 28, 1940, and assigned to the assignee of this application. This application has issued as Patent 2,329,132.

One of the major problems confronting the electrical industry is that of distributing, satisfactorily, alternating current to consumers in urban and medium density areas. Such distribution must not only provide reliable and continuous service, but the cost of the distribution system must justify its installation.

For more than ten years the most reliable alternating current distribution system for heavy density or urban areas has been that known as the Palmer system. In this system a plurality of high voltage primary feeder circuits are employed for supplying energy to a common lowvoltage secondary network or grid circuit. Each of the feeder circuits is connected to the common network circuit through a plurality of network transformers and network protectors. Each of the protectors includes a directional relay for controlling the operation of the network protector. When a fault occurs on the network circuit, the flow of current to the fault does not actuate the directional relays and the fault is burned clear. The amount of energy available from the feeders is so large that generally no difliculty is encountered in burning clear faults occurring on the network circuit.

When a fault occurs on a feeder circuit, the flow of current through the directional relays associated with the feeder circuit actuates the relays and trips the network protectors to disconnect the faulted feeder circuit from the network circuit. The sound feeder circuits continue to supply energy to the network circuit and substantially no impairment of service results from a fault occurring on any feeder circuit.

Although the Palmer type network distribution system provides service of excellent reliability and continuity, its costs has justified its adoption only in areas having a heavy density of energy consumption such as the areas occurring in large cities.

At present a large proportion of electrical energy is supplied to medium density areas through radial systems. Such systems are relatively low in cost but are unsatisfactory because of the unreliability of the service which they offer. For example, a failure of a single feeder in a radial system results in an inconvenient outage for the entire distribution circuit supplied by the feeder.

An alternative service is provided in a system described in Patents 1,979,353, 1,979,703 and 2,023,096. In this system, the network protectors of the conventional l-aimer system are replaced by low cost sectionalizing switches which open only when the system 15 deenergized. To this end, when a fault occurs on a feeder circuit the feeder circuit breakers open to deenergize completely the entire system. After the feeder circuit breakers open, the sectionalizing switches associated with the faulted feeder also open. When the feeder circuit breakers reclose, only those sectionalizing switches associated with the sound feeders are closed.

Such a system may be installed at a relatively low cost. However, although the outages from such a system are of shorter duration than those encountered in a radial system of distribution, they affect a larger number of customers and occur more frequently for the reason that a fault on any feeder results in a short outage for the entire system. A second disadvantage of this ssytem is that the feeders cannot be relied upon to supply radial loads or conventional network circuits connected in parallel with the simplified network shown in the aforesaid patents. These factors substantially restrict the field of application for this system.

In accordance with this invention, the conventional common network circuit or grid is replaced by a plurality of substantially independent secondary loop circuits. A plurality of primary feeder circuits are employed for supplying electrical energy through a plurality of network transformers to each of the loop circuits and the connections between the feeder circuits, and each of the loop circuits are so disposed that when any feeder circuit is removed from service the load on the loop circuit is distributed uniformly among the transformers associated with the remaining feeder circuits. By providing independent loop circuits, it is possible to isolate any loop without removing other loop circuits from service. Moreover, in starting operation on a dead or deenergized distribution system, it is possible to add loop circuits to the system successively as the condition of the system permits.

A further aspect of this invention comprises the replacement of the Palmer type network protector by inexpensive, rugged switches. Each of the network transformers is connected to its associated loop through a network switch which is designed to open only when substantially no current flows therethrough. Between each pair of network transformers a sectionalizing switch is placed in the loop circuit. The sectionalizing switches open in advance of the network switch when a fault occurs on a feeder circuit associated therewith. Since the feeder circuit also opens,

the network switch is completely deenergized before it opens. Since the network switch does not open a circuit carrying current, its design may be appreciably simplified, and the network switch may, if desired, be placed in the casing of its network transformer. Moreover, due to the usual location of the sectionalizing switches midway between the two adjacent transformers, the fact that load is tapped off along the secondary loop circuit, and the fact that the transformer currents fiow two ways from the transformers in the secondary loop circuit, each sectionalizing switch requires a current capacity of only 50 to 75% of the current rating of the largest adjacent network transformer.

If a switching system designed in accordance with this invention were applied to a conventional network circuit, one network switch and about one and one-half sectionalizing switches would be required for each network transformer. However, with the loop system, only one network switch and one sectionalizing switch are required for each network transformer. As above indicated, the design and relaying of these switches may be appreciably simpler than that provided in the conventional network protector.

It is, therefore, an object of this invention to provide a network switch of simple and rugged design.

It is a further object of this invention to provide a network switch which closes only if the phase conditions across its contacts are correct.

It is a further object of my invention to provide an improved phasing control for distribution switches.

Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is a single-line diagrammatic view of a network distribution system;

Fig. 2 is a single-line diagrammatic view of a modified network distribution system;

Fig. 3 is a single-line diagrammatic view of a modified network distribution system embodying this invention;

Fig. 4 is a diagrammatic view of a sectionalizing switch suitable for the system illustrated in Fig. 3;

Fig. 5 is a diagrammatic view of a network switch embodying this invention which is suitable for the system illustrated in Fig. 3;

Figs. 6, 7, 8 and 9 are diagrammatic views showing modifications of the network switch illustrated in Fig. 5;

Figs. 9a, 9b, 9c and. 9d are diagrammatic views showing vector relationships for the network switch of Fig. 9.; and

Fig. 10 is a diagrammatic view of a further modification of a network switch.

Referring to the drawings, Fig. 1 represents a conventional Palmer type network distribution system. In this particular system, three feeders l, 2 and 3 areshown for supplying electrical energy from one or more sources, here represented by a bus 4, to a common network circuit or rid 5. Each of the feeder circuits is provided with a feeder circuit breaker la, 2a and 3a for controlling the connection to and disconnection from the bus 4 of the feeder circuits. The feeder circuits also are connected through network transformers lb, 2b and 3b, which may be of the high reactance type, and through network protectors 6 to the network circuit 5'. In order to keep down the spare transformer capacity required, it is the practice to interlace the feeder circuits as thoroughly as possible as illustrated in Fig. 1. It should be noted further that the entire network circuit 5 is rigidly connected together.

When a fault occurs on the network circuit 5, the fault is burned clear with no operation of the network protectors 6. the high reactances of the network transformers prevent excessive feeder circuit currents from flowing.

If a fault occurs on one of the feeder circuits such as the feeder circuit l, the directional relays of the network protectors 6 associated with all of the network transformers lb operate to disconnect the feeder I from the network circuit 5. In addition, the feeder circuit breaker la opens to disconnect completely the feeder circuit I from both the bus 4 and the network circuit 5. Energy for the network circuit then is supplied over the remaining feeder circuits 2 and 3. A more complete description of the network protectors and the operation of the system illustrated in Fig. 1 may be found by reference to my Patents 1,973,- 097, 1,997,597 and 2,013,836, which illustrate typical network relays and their operation.

As above explained, a system similar to that illustrated in Fig. 1 is excellent from the standpoint of reliability and service continuity. Its principal drawback is that of cost.

In Fig. 2, a network distribution system is 11- lustrated which departs somewhat from the conventional Palmer system. In Fig. 2 the feeder circuits l, 2 and 3 are connected through their associated network transformers lb, 2b and 3b to a plurality of substantially independent low-voltage loop circuits 1, 8 and 9. These loop circuits may be of the same dimensions or of different dimensions as illustrated by the short loop circuit 9 of Fig. 2. The various network transformers may be connected to the loops through network protectors 6 which may be of the conventional Palmer type illustrated in my aforesaid patents. It will be understood that consumers of electrical energy are supplied with service from the various loop" circuits.

To assure a uniform distribution of load among the various network transformers under different conditions, the network transformers are preferably connected to each loop circuit in an orderly sequence as illustrated in Fig. 2. Moreover, in each loop circuit the impedance of the loop circuit between any pair of adjacent network transformers is substantially equal to that of the loop circuit between any other pair of,

such as those illustrated in my aforesaid patents Under these conditions,

provide ideal operation of the loop system illustrated in Fig. 2, such protectors are designed to open circuits carrying substantial current and their design is somewhat complicated. and expensive. In order to simplify and reduce the cost of the network system, I have developed a complete new switching sequence which is illustrated a diagrammatically in Fig. 3.

Referring to Fig. 3, a plurality of loop circuits l1, l8 and H), which correspond to the loop circuits 1, 8 and 9 of Fig. 2 are energized from the three feeder circuits l, 2 and 3 through the network transformers lb, 2b and 3b. However, in place of the network protector 6 of Fig. 2, I provide a transformer or network switch It! which is designed to open a circuit carrying substantially no current.

Before actuation of the network switch ill to its open condition, the network switch I is first isolated from any sourceof current. For this purpose each network switch I0 is separated from adjacent network switches by means of section alizing switches ll. When a fault occurs on any feeder circuit such as the feeder circuit I, the sectionalizing switches il adjacent each of the network transformers l b open in response to the excess flow of current from the loop circuits to the faulted feeder circuit. In addition, the feeder circuit breaker Ia also opens and completely deenergizes the network transformers lb and the network switches l0 associated therewith. The network switches I!) are responsive to the deenergized condition of the associated network transformers lb and open with substantially no current flowing therethrough.

Preferably, the sectionalizing switche il close automatically after a time delay to restore the loop circuits to their original condition for energization from the sound feeder circuits 2 and 3. Under this condition of energization the load on the loop circuits is divided evenly among the network transformers 2b and 37).

If a fault occurs on a loop circuit, it is desirable that the fault burn clear without necessitating the tripping of any network switch or sectionalizing switch. Since most faults occurring on a network circuit or 100p circuit clear in approximately one or two seconds, by providing the sectionalizing switches I I with a suitable time delay, faults occurring on the loop circuits are permitted to burn clear.

In Figs. 2 and 3, certain circuits are illustrated by diagonal lines. This illustration is for the purpose of facilitating the tracing of circuits and has no other significance.

The loop circuits illustrated in Figs. 2 and 3 may be either single-phase or polyphas-e. If sin gle-phase they may be energized from a singlephase source or from a polyphase source. For example, if single-phase loop circuits are connected for energization from a three-phase source, one-third of the loop circuits would be connected for energization from each phase of the three-phase source. In such a system, by employing single-phase feeder circuit breakers, a failure of any phase will not impair service on the remaining operative phases.

If the switching system illustrated in Fig. 3 were employed on a conventional network or grid circuit, it would follow that substantially one network switch I!) and one and one-half sectionalizing switches H would be required for each I network transformer. By adoption of the loop circuits illustrated in Figs. 2 and 3, this requirement is cut to one network switch Hi and one sectionalizing switch H for each network transformer.

As above indicated, a sectionalizing switch is located between two network transformers. Because of its location, the capacity of the sectionalizing switch need be only 50 to of the capacity of the largest of the two adjacent network transformers. The sectionalizing switch is designed to trip for a flow of power in either direction therethrough. Moreover, the sectionalizing switch is designed to reclose when a suitable voltage is present on either side of the switch. A suitable construction is illustrated in Fig. 4.

Referring to Fig. 4, the sectionalizing switch I l includes a circuit breaker 64 for connecting two portions of the loop circuit IT. The circuit breaker 6 3 is maintained in a closed position by means of a latch 65 which is pivoted for rotation about a point 66. The latch 65 is provided with two tripping legs 61 and 68 which are positioned in the paths of travel of two thermal elements 59 and 10. These thermal elements are designed to be heated by current flowing in the conductors of the loop circuit I'l. Although heat for the thermal elements may be provided in various manners, in the illustration, current passing through the conductors of the loop circuit l1 passes directly through the heaters of the thermal elements. As the thermal elements heat, they tend to rotate about fixed supports H and into engagement with the tripping legs 61 and 623. The thermal elements may take various forms, but as illustrated, they are bimetallic elements.

Excessive current may flow through the heaters for the thermal elements either for an internal loop circuit fault or for an external feeder circuit fault. Ordinarily it is desirable that internal or loop circuit faults burn themselves clear. Most of these internal faults will burn clear in one or two seconds. Consequently, the thermal elements 69 and iii are provided with a time delay, preferably an inverse time delay, with a minimum operating time of two to two and one-half seconds when maximum current flows to a fault occurring in the secondary or loop circuit I1. This provides adequate time for clearance of the usual secondary or loop circuit fault. The thermal elements 59 and 10 may be adjusted to trip the circuit breaker 64 in response to current in excess of 60 to of the full load current of the larger of the two network transformers adjacent the sectionalizing switch II.

For automatically closing the sectionalizing switch I I, it is desirable that the circuit breaker 64 close when suflicient voltage is present on either side of the circuit breaker. To this end a transfer relay '13 is provided for energizing the closing circuit of the circuit breaker 64 from either side of the circuit breaker. In the form illustrated, the transfer relay includes a solenoid M which is connected for energization in accordance with the voltage present on one side of the circuit breaker 64. This transfer relay is adjusted to pick up and close its front contacts when energized by a voltage greater than '70 to 75% of normal. It is designed to drop and engage its back contacts when the energizin voltage drops below 25 to 50% of normal. The front contacts are connected to the loop circuit I! on one side of the circuit breaker 64 and the back contacts are connected to the loop circuit 11 on the opposite side of the circuit breaker B4. In

the form illustrated, the transfer relay 13 is pro- 7 videdwith a, movable. contact. member having two insulated contacts 15 and 16 for selectively engaging the; front or back contacts of the relay. The movable contacts I15. and t6. are connected through suitable conductors TI: and I8 to energize the closing mechanism of the circuit breaker 6.4.. It will be. observed that. if the voltage applied to the Solenoid [4 is in excess of 7.0. to. 75% of normal,. the conductor I1 and I8 are. connected, respectively, to the conductors of the loop circuit II on the, right of the circuit breaker 64'. If; the voltage applied to. the solenoid 1.4, drops below to 50% of normal, the conductors I1 and. 18' are. connected, respectively, to the condoctors of the loop circuit on the left of the circuit break-er 64. Consequently, the closing circult for: the circuit breaker will be energized even thou h either portion of the loop circuit is dener ized.

Reclosure of the circuit breaker 64 is effected through a, closing motor or solenoid 19. The closing circuit for the solenoid 19 may be traced from the movable contact 15 through the conductor Tl, a conductor 80, contacts of a closing relay 8 I, a fuse &2, thesolenoid 19, a pallet switch 0,3. carried by the circuit breaker 6.4, and the conductor I8 which is connected to the second movable contact 16. V

In order to provide adequate time for operation of the network switches, l0, it is desirable that the circuit breaker 64. be closed only after the expiration of a suitable time delay such as four to six seconds. In the embodiment illustrated in Fig. 4, this time delay is provided by the thermal elements 59 and I which have back contacts 84 and 85. After an actuation of either of the thermal elements 69 and I0 into tripping condition, a delay of four to six seconds is required before the thermal elements reengage their back contacts Mv and 85. These back contacts are included in the closing circuit for the circuit breaker 64. g

The energizing circuit for the closing relay 8| may be traced from the movable contact I through the conductor TI, a conductor 86, the back contact 84 a conductor 81, the back contact I35, a conductor 88, the solenoid of the closing relat 8i, the pallet switch 83 and the conductor 18 back to the second movable contact I6. This closing relay 3| is adjusted to close its front contacts, and seal itself closed, in response to a voltage above approximately 80% to 85% of normal.

When the closing relay 8| operates to close its front contacts, it establishes a closing circuit for the closing solenoid 19, as above described.

If a fault occurring on the secondary or loop circuit I! should persist for more than two or two and one-half seconds, the circuit breaker 5H closes and trips at intervals of approximately six to eight seconds. If it is desired to eliminate excessive operation or pumping of the circuit breaker 64 under these circumstances, a fuse 82 may be included in the closing circuit of the circuit breaker. This fuse may be so proportioned that it blows and opens the closing circuit after six to twelve immediately consecutive operations of the circuit breaker 64 in response to the cumulative intermittent energization thereof. This should provide ample opportunity for any usual secondary or loop circuit fault to burn itself clear.

The network switch I0 is designed to open only when substantially no current flows there? through. A suitable construction for this purpose is illustrated in Fig. 5, wherein a circuit breaker aaeoeio m0; employed" for controllingthe connection of the network transformer lib to a loop. circuit. The circuit breaker I00 is latched in its closed position by means. of a. suitable tripping lever I01, which is. pivoted for rotation about a fixed; axis. I02. A spring 103 is employed for biasing the. tripping lever IOI towards its tripping 1 05i; tion against a stationary stop. I04.

Under normal conditions of operation, the tripping lever I-[tl is maintained in its latching posi-.

tion by means of a voltage responsive solenoid I05, which is connected across the secondary of the network transformer Ibthrough the front contacts of a, pallet switch I06 carried by the cir-, cuit breaker. The solenoid I 05 is so designed that when the voltage thereacross falls, below,- approxi-. mately 25 to 30% of its normal value, the spring I03 rotates the tripping lever I01 into. its tripping posit on- 7 Referring to Fig. 3. when t sectionalizing switch II adjacent a network switch [0, associated with a transformer Ib open, and when; the. feeder circuit breaker Ia opens in response to a fault occurring on the feeder circuit I, the net: Work switch I0 is completely deenergized. Under these conditions, the voltage across the solenoid I05 of Fig. 5 drops below 2 to 30% of its normal value, and the circuit breaker lei) trip to dis,- connect the transformer Ib from its loop. circuit. It should be noted that under these conditions substantially no current flows through the circuit breaker I00.

If t t p f the rcuit breaker I0". is controlled only by an u derv ltage c n ol device. the circuit breaker may open when carrying sub7 tant a r nt under som faul co dit ons. For

am w nc fau t oc u a oo circuit adj cent the ci cu t b ea e H ll. th vo a e ac ss t e o enoid 6 ma fa l w ll below 25 o 30% of its n mal value. Con e ent th circuit breaker I00 will trip while carrying the full fault current. If the circuit breaker is designed for such operation, no harm results. however, s a ove e plain it s desirable tha he circuit breaker I00 open only while Carrying substan,

tially no current. It is also desirable that cuit breaker I00 remain closed so that tr former I6 may supply current to the fault to assist in burning it clear. To this end, a currente responsive device is provided in Fig. 5 for assist: ing the solenoid I05.

The current-responsive device may take the form of two electromagnets I07 and I08 which control a link I09 pivotally attached to the tri ping lever IOI by means of a pin H0. Each of the electromagnets may comprise a Ueshaped magnetic member I I I which may be of laminated soft iron or steel. Each of the u-shaped magnetic members is positioned with its legs substan: tially surrounding one of the main conduetgrs associated with the secondary of the network transformer Ib. Each magnetic member III is provided with a magnetic armature IIZ attached. to the link me. The electromagnets I01 and I08 may be so designed that with current in excess of three f ve times normal rated load current flowing throngh the circuit breaker I00 and with zero voltage across the solenoid I05, the tripping lever ,I0liis maintained in its latching position against t e bias of the spring I03. The electrom'agnets III and solenoid I05 cooperate to prevent opening of the circuit breaker L00 when substantial cur.- rent flows therethrough. This greatly facilitates the placement of the network switch I0 and the network transformer lb in a common casing, represented in Fig. 5 by a broken line H3. The circuit breaker l may be immersed in the insulating and cooling liquid employed for the transformer lb.

For maximum economy, the network switch l0 may be provided only with a manual reclosing structure. For completeness, however, I have illustrated in Fig. a simple reclosing mechanism therefor. Generally, a reclosing mechanism is preferable. In Fig. 5, the circuit breaker I00 is provided with a closing motor or solenoid H4 which may be connected across the secondary of the transformer lb through the front contacts of a timing relay H5 and the back contacts of a pallet switch ll6 carried by the circuit breaker. When the circuit breaker trips, the back contacts of the pallet switch l l6 close to connect the operating coil ll! of the timing relay 5 across the secondary of the network transformer lb. At the end of a predetermined time delay, such as three to six seconds, the front contacts of the timing relay close to connect the closing solenoid ll4 across the secondary of the transformer. The parts may be so proportioned that the circuit breaker closes with a three to six second time delay when voltage in excess of approximately 9 of the normal voltage appears across the secondary of the transformer. The time delay is provided for proper cooperation with a reclosing feeder circuit breaker, and this cooperation will be set forth more particularly in connection with Fig. 8.

As above indicated, the network switch l0 may be made manually reclosing for maximum economy. When a tripping mechanism. similar to that illustrated in Fig. 5, is employed, satisfactory operation of the network switch I0 is assured, but under some conditions certain inconvenience may result from operation thereof if manual reclosing is used. Referring to Fig. 3, let it be assumed that all sources of energy connected to the bus 4 are intentionally disconnected. Under these conditions, the entire network distribution system is deenergized, and all of the network switches l0 trip to disconnect the deenergized feeders from the associated loop circuits. If these network switches ID are of the manual reclosing typ each switch must be manually reclosed when the network distribution system is again placed in operation. The manual reclosing of each network switch l0-results in substantial inconvenience and unnecessary delay in the restoration of service.

In Figs. 6 and '7, a manual reclosing network switch H1 is illustrated which does not trip when the entire network distribution system is deenergized due to failure of the power supply to bus 4, Fig. 3. This network switch includes a circuit breaker I00, which is similar to the circuit breaker I00 of Fig. 5 except for the omission of the reclosing mechanism. The tripping of the circuit breaker I00 is controlled by a tripping lever l0! which corresponds to the tripping lever l0l of Fig. 5, and which is controlled by the electromagnets I01 and l 08 and by the solenoid I05 described with reference to Fig. 5.

Tripping of the circuit breaker I00 when the entire distribution system is deenergized is prevented by a roller 8 which is carried by a bell crank l H! pivoted for rotation about a stationary axis I20. A spring l2l is provided for biasing the bell crank H9 in a clockwise direction about its axis towards a fixed stop I22. When the circuit breaker I00 is manually closed, the roller ll 8 travels along a curved guide extension I23 carried by the tripping lever l0l' from the position illustrated in Fig. 6 into the position illustrated in Fig. '7, wherein the bell crank H9 is against the stop I22. With the parts in the positions illustrated in Fig. 7, the roller ll8 prevents movement of the tripping lever I0 I to tripping position, even though the electromagnets l0! and I08 and the solenoid l05 are completely deenergized. Consequently, the tripping lever l0l retains the circuit breaker I00 in its closed condition, even though the distribution system is completely deenergized.

In order to permit tripping of the circuit breaker I00 when a fault occurs on the feeder circuit l, a current-responsive device is employed for actuating the bell crank ll9 away from its stop l22. This current-responsive device may take the form of a thermal element, such asa bimetallic thermal element l24 carried by a stationary support I25. When this thermal element is heated, it is designed to move from the full-line position illustrated in Fig. 6 to the position illustrated in dotted lines. In so moving the thermal element rotates the bell crank I IS in a counterclockwise direction to carry the roller ll8 away from the tripping lever l0l. Following such movement of the roller N8, the tripping lever l0l is controlled only by the electromagnets I01 and I08 and the solenoid I05 in the manner described with reference to Fig. 5. The thermal element l24 may be heated in any desired manner. As illustrated, a heating coil l2'l is connected directly into one of the conductors associated with the secondary of the transformer lb.

The thermal element I24 may be so designed that it carries one and one-half to two times the full load current of the network switch without actuating the bell crank H9. The design is such that, with three tofour times the full rated load current of the network switch flowing therethrough, the thermal element actuates the bell crank ll9 to release the tripping lever l0l' in approximately one and one-half to two seconds.

Under normal load conditions and when the entire system is deenergized, th roller 8 remains in the position illustrated in Fig. 7 to prevent trip;

ping of the circuit breaker I00. When a fault occurs on the feeder circuit drawing three to four times rated load current of the network switch, the thermal element I24 operates in one and onehalf to two seconds to release the tripping lever l0l'. Such release of the tripping lever does not necessarily result in tripping of the circuit breaker I00. Such tripping takes place only if the voltage across the solenoid I05 and the current through the electromagnets I01 and I08 are below predetermined values. With such a construction, the circuit breaker I00 trips only when carrying substantially no current, and does not trip when the entire distribution system is deenergized. It should be noted that after an operation, the thermal element returns to its full line position with a time delay due to the inherent cooling properties thereof. In the system illustrated, the time delay is ample to permit satisfactory tripping.

In Fig. 8 another suitable network switch I0 is illustrated. In the figure, a network transformer lb having fuses J for its primary winding is illustrated for supplying a three-wire, single-phase loop circuit. The network transformer lb is connected to a loop circuit through a network circuit breaker 25. Under normal operating conditions, this circuit breaker is held in its closed position the three-phase system which corresponds to the circuit breaker of Fig. 8 and is controlled by the same latching mechanism illustrated in Fig. 8. In Fig. 9, however, the current solenoid 29 is energized from a single current transformer 52, and the voltage solenoid 30 is energized from one phase of the secondary of the network transformer lb, The energizing circuit for the voltage solenoid 30 may be traced from a conductor 53 through the voltage solenoid 30, front contacts of a pallet switch 32a carried by the circuit breaker, a conductor 54 and a conductor 55. The operation of the latching mechanism is similar to that described with reference to Fig. 8. In Fig. 9, the parts 25a, 32a, 38a and 39a correspond to the parts 25, 32, 38, and 39 of Fig. 8.

The circuit breaker 25a of Fig. 9 may be manually reclosed but preferably, as illustrated, an automatic reclosing system is employed. This reclosing system employs the timing relay 42 of Fig. 8 which is energized, in Fig. 9, through a circuit which may be traced from the conductor 55 through the solenoid 44 of the timing relay, the back contacts of a phasing relay56. a conductor 51, the back contacts of the pallet switch 39a and a conductor 58. The timing relay 42 consequently is responsive to the voltage across one phase of the three-phase circuit and operates in the same manner discussed with reference to Fi 8.

Although a phasing system need not be employed in Fig. 9, a phasing relay 56 is illustrated for completeness. This relay 55 is energized in accordance with the outputs of two positive phase-sequence voltage filters 59 and 60. positive phase-sequence voltage filter 59 is connected on the transformer side of the circuit breaker 25a and is connected to provide an out put proportional to the positive phase-sequence voltage of the feeder circuit. The positive phasesequence voltage filter B8 is connected on the network or loop circuit side of the circuit breaker 25a and is connected to have an output proportional to the positive phase-sequence voltage of the network or loop circuit, The outputs of the voltage filters are connected so that the phasing relay 56 is energized by the difierence of the output voltages of the two filters 59 and 60, If,

The

during repairs of the feeder circuit I, hase conductors are interchanged, the outputs of the two positive phase-sequence voltage filters are no longer substantially equal and in phase, and the phasing relay 55 opens its contacts to prevent closure of the circuit breaker 25a.

The construction of the positive phase-sequence voltage filters may be similar'to that illustrated in the Lenehan Patent No. 1,936,797. Each of these voltage filters comprises, in general, an auto-transformer 6! having a tap Ela, a resistor 62 and a reactor 63. The various elements of each filter are so related that the voltage drop across the resistor 62 is equal to the same percentage of the total voltage impressed on the resistor 62 and the reactor 63 in series as the ratio of the auto-transformer 6|, but lags the total voltage impressed on the resistor and reactor by 60. Assuming the phase rotation of the three-phase system to be in the order, a, b, c, as indicated in Fig. 9. the outputs of the voltage filters will be proportional to the desired positive phase-sequence voltages.

The relay for controlling the closure of the circuit breaker 25a on a dead network or loop circuit also is employed in Fig. 9.

It should be noted that the phasing system illustrated in Fig. 9 provides complete phasing protection for a network switch with only one relay 56. The only parts required in addition to the relay are two simple voltage filters 59 and 60. The. operation of the phasing system illustrated in Fig. 9 will be explained further with reference to Figs. 9a and 9d, which show vector representations of voltage conditions in the voltage filters for various conditions of the feeder circuit. In these figures the reference characters a, b, c designate physical points based on the normal condition in Fig. 9a.

In Fig. 9a, vector relations are shown for the voltage filters when both the feeder circuit l and the network or loop circuit are properly connected and energized. Under these conditions, the line voltages applied to the voltage filter 59 may be represented by three vectors ac, ab and be, the direction of rotation of these vectors being counter-clockwise, as indicated by the arrow. The voltage cb is applied across the autotransformer SI of the voltage filter 59 and this is represented in Fig. 9a by superimposing the auto-transformer on its voltage vector. Similarly. the voltage vector ha is applied across the resistor 52 and the reactor 63 connected in series, and the resistor and the reactor are indicated in Fig. 9a as superimposed on their respective vector components. With the condition as illustrated in Fig. 9a, the output of the voltage filter 59 is a vector E.

The vector conditions for the voltage filter are similar to those illustrated for the voltage filter 59. Consequently, the voltage output of the filter 60 may be represented by a vector E. which is substantially equal in magnitude and direction to the vector E.

The connections for the relay 56 are illustrated in Fig. 9a in dotted lines. It will be noted that the outputs of the voltage filters 59 and 60 are connected in the circuit for the relay 56 in ,phase opposition. Consequently, substantially no current flows through the relay 56 and the relay remains closed to permit closure of the circuit breaker 25a.

If two of the phase conductors of the feeder circuit 5 are interchanged during repairs, the circuit breaker 25a should not close. The vector relations in the filter 59 for such a condition are illustrated in Fig. 9b, wherein it is assumed that the phase conductors c and b are interchanged.

The eifect of such an interchange of the conductors c and b is to reverse the voltage across the auto-transformer 6|. This reversal is indicated in Fig. 92) by reversing the representation of the auto-transformer. Moreover, the effect of such an interchange is to rotate the voltage applied across the reactor 63 and the resistor 62 by measured in the clockwise direction, as illustrated in Fig. 91). From an inspection of these vector relations it will be noted that the vector Ea, which corresponds to the vector E of Fig. 9a,, is reduced substantially to zero. Since the output voltage E of the voltage filter 60 remains unchanged, it follows that a substantial resultant voltage E is applied across the relay 56, and the relay consequently picks up to prevent closure of the circuit breaker 25a. In other words, the interchange of the two conductors c nd 1) results in the application of a system of voltages to the voltage filter 59, which rotates in a direction similar to the rotation of a system of negative phase sequence vectors. Since the voltage filter 59 is designed to pass only a quantity dependent upon a positive phase sequence system of vectors, it follows that the voltage output Ea of the voltage filter '50 is substantially zero for the conditions assumed in Fig. 9b. I

"If in repairing the feeder circuit I, all three phase conductors are advanced 120, the effect on the voltage filter 59 may be represented by rotating all of the vectors of Fig. 9a by 120". This is illustrated in Fig. 9c.

Referring to Fig. 90, it will be noted that the output voltage of the filter 50 is represented by a vector Eb, which is substantially equal in magnitude to the vector E of Fig. 9a but differs in phase therefrom by 120. Since the vector E representing the output of the voltage filter remains unchanged, it follows that the resultant of the voltages E and Eb is of substantial magnitude'and causes the relay 56 to pick up and prevent closure of the circuit breaker 25a.

If in repairing the feeder circuit I, all three phaseconductors are rotated 240, the conditions in the filter 59 may be represented by rotating the vectors in Fig. 9a by 240. in Fig. 9d.

The voltage output of the filter 50 in Fig. 9d is representedby a vector Ec which is substantially equal in magnitude to the vector E of Fig. 9a,'but differs in phase therefrom by 240. Since the vector E representing 'theoutputof the voltage vector '50 remains unchanged, 'the resultant of the vectors E and E0 represents a substantial voltage across the relay 56 and the relay picks up to prevent closure of the circuit breaker 25a.

In the network switches thus far described, a current-responsive control member is employed for preventing the tripping of the circuit breaker when a fault occurs adjacent thereto on the associated loop circuit. By proper compensation o'fthe voltage applied to the solenoid'l05 of Fig. 'or '7, it is possible to control the tripping of the circuit breaker by means of the solenoid alone. Fig. 10 illustrates such a construction wherein a single solenoid I28 is employed for controlling a tripping lever I for a circuit breaker I30. The solenoid I28 may be energized from the secondary of the network transformer lb in accordance with the voltage present on the feeder circuit I. For this purpose, a compensator I3I, illustrated as consisting of an adjustable resistor I32 and an adjustable reactance I 33, is energized in accordance with the current flowing in the secondary of the network transformer by means of two current transformers I34 and I35. The impedance of the compensator l3l is so proportioned that the current flowing therethrough produces a voltage drop thereacross which is proportional to the voltage drop across the transformer I b. The energizing circuit for the solenoid I28 may be traced from one terminal of the transformer sec- 'ondary through a conductor I3, the front contacts of a pallet switch I31 carried by the circuit breaker, a conductor I38, a resistor I39, the energizing coil of the solenoid I28, a conductor I40, the compensator I3I and a conductor I4I to the other main terminal of the secondary winding. From an inspection of this circuit it will be noted that the voltage across the solenoid I20 is proportional to the secondary voltage of the transformer plus the voltage represented by the drop across the compensator I3I. Consequently, the solenoid I28 will be energized in accordance with the voltage present on the feeder circuit I.

Should a fault occur on a loop circuit adjacent the circuit breaker I30, the voltage across the secondary of the transformer lb may drop to a negligible value. However, the voltage drop This has been done across the compensator I3l rises to a substantial value corresponding to the drop across the transformer Ib, and the solenoid I28 consequently will remain energized by a substantial voltage. With a fault on the loop circuit, the voltage on the feeder circuit I rarely falls below approximately 50% of its normal value. Such a valueis well above the voltage dropout setting for the solenoid I28, which may be 25 to 30% of normal voltage. When the network transformer and the adjacent sections of the loop circuit II are completely deenergized, the voltage across the solenoid I28 falls below 25 to 30% of the normal feedercircuit voltage, and the spring I03 operates to move the tripping lever I20 to its tripping position.

Under the conditions thus far described, the circuit breaker I30 may trip while carrying substantial current. For example, if a fault-occurs on the feeder circuit I adjacent the network transformer 'Ib, the voltage across the solenoid I28 may drop to a low value, thereby permitting the circuit breaker I30 to trip. Such tripping would be under conditions wherein the circuit breaker carries substantial current. Here again, suc'h'tripping is permissible if the circuit breaker is designed for such operation, but preferably the controls should be such that the circuit breaker does not open while carrying substantial current.

To prevent this undesirable operation of, the circuit breaker I30, a relay I42 may be provided for short-circuiting the compensator I 3I. This relay I42 is energized in accordance with the voltage across "the secondary of the network transformer Ib. When the voltage applied to the relay I42 rises above a predetermined value, the relay picks up to close its front contacts, thereby short-circuiting the compensator HI and energizing the solenoid I28 in accordance with the voltage across the secondary of the transformer 'I b. While the voltage across the secondary of the transformer is above the dropout value for the relay I42, the solenoid I28 is energized in accordance with the secondary voltage'to maintain the tripping lever I29 in its latching position.

If a fault occurs on a secondary loop circuit adjacent the circuit breaker I30, the voltage across the relay I42 may drop to substantially zero. Consequently, the relay I42 opens its contacts to place the compensator I3I in operation. Because of the operation of the compensator, the voltage across the solenoid I28 becomes propor-j tional to that present in the feeder circuit l, and the circuit breaker I30 consequently does not open as long as this voltage is present.

Should a fault occur on the feeder circuit l, the voltage across the secondary of the transformer lb remains above the dropout setting for the relay I42. The solenoid I28 continues to be energized in accordance with the voltage across the secondary of the transformer lb, and this is sufficient to prevent tripping of the circuit breaker I30.

Preferably, the dropout voltage for the solenoid I28 should be as low as possible when employed with the relay I42. For example, a dropout at 10 to 15% of normal voltage is preferable to a dropout at 25 to 30% of normal voltage. This may be obtained by making the resistor I39 of a material having a high positive temperature coefiicient of resistance. Such a resistancemay be obtained by employing tungsten therefor in the form of one or more lamps. The relay I42 may have a dropout setting approximately 5 to 10% above the maximum dropout voltage of the solenold I28. In order to assure dropout of the relay M2 in advance'of operation of the solenoid I28, the Solenoid may be provided with a slight time delay in its tripping direction.

From the foregoing discussion it is believed that the operation of a distribution system similar to that disclosed in Fig. 3 is apparent. Assuming that the system is in operation and energized from all three feeders, each of the loop circuits I 1, l8 and I9 carries load in a manner analogous to that of the conventional secondary network circuit. If a fault occurs on any of the loop circuits, current is supplied to the fault for a period of two to two and one-half seconds. If

the fault fails to burn itself clear within this period the sectionalizing switches adjacent the fault trip. About four to six seconds later these sectionalizing switches reclose and remain closed for another two to two and one-half seconds. If the fault again fails to burn itself clear, the sectionalizing switches again open and continue to"pump for approximately six to twelve cycles at which time the fuses 82 associated with these sectionalizing switches blow to prevent further closure thereof. The sound portions of a loop circuit then continue to supply load to all but a small portion of a load adjacent the fault.

If a network transformer directly connected to the faulted section of the loop circuit is provided with fuses having a long time delay so that the sectionalizing switches will trip first on any fault, the fuses will blow if the loop fault fails to burn clear within the time provided by the fuse setting.

If a fault occurs on one of the feeder circuits such as the feeder circuit l, at the expiration of the two to two and one-half seconds minimum, the sectionalizing switches adjacent each of the network transformer switches lb open to disconnect the feeder circuit I from the remainder A of the loop circuits. In addition, the feeder circuit breaker la, which is provided with a conventional tripping control, opens to deenergize completely the feeder circuit l, the network transformers lb and the network switches Hi. The network switches ID in response to this deenergization trip to disconnect the feeder circuit I from the loop circuits.

At the expiration of four to six seconds the sectionalizing switches ll adjacent each of the network transformers lb reclose to restore the loop circuits to their original condition, The entire loop circuits then continue to supply load from the network transformers associated with the sound feeders 2 and 3, the load being uniformly distributed among these network transformers.

Following its tripping the feeder circuit breaker la promptly recloses. If the fault on the feeder circuit has cleared itself prior to the reclosure, the feeder circuit breaker remains closed. At the expiration of approximately three to six seconds the network switches l0 associated with the network transformers lb reclose to restore full service to the loop circuits l1, l8 and I9.

If the fault on the feeder circuit l fails to clear prior to the first reclosure of the feeder circuit breaker la, the feeder circuit breaker again trips prior to reclosure of the network switches associated with the network transformers lb. After the expiration of ten seconds, the feeder circuit breaker la again closes. If the fault has cleared in the meantime, the network switches Ill associated with the network transformer lb close at the expiration of three to six seconds to restore full service for the loop circuits. Assuming that the fault has not cleared, the feeder circuit breaker la again trips out and at the expiration of fifteen seconds the same cycle is repeated.

After three reclosures, if the fault persists, the feeder circuit breaker la is permanently locked out and the feeder circuit l is permanently disconnected from the bus 4 by the feeder circuit breaker la and from the loop circuits by the associted network switches l0. Automatic reclosing feeder circuit breakers of this type are well known in the art.

Although the system illustrated in Fig. 3 does not offer a continuity of service fully equal to that of the system illustrated in Fig. 1, it is a great improvement over the radialsystem of distribution and is an economical system to install.

If desired, an artificial fault may be established for a feeder circuit by an opening of a feeder circuit breaker in order to ensure operation of all network switches associated with the feeder circuit whenever the feeder circuit breaker opens. This is represented in Fig. 8 by a switch P. A closure of this switch, either manually or by opening of the feeder circuit breaker, establishes an artificial fault across the feeder circuit I through a suitable current-limiting impedance Z.

Although I have described the invention with reference to certain specific embodiments thereof, numerous modifications thereof are possible. Therefore, I do not desire the invention to be restricted except as required by the appended claims when interpreted in view of the prior art.

I claim as my invention:

1. In a polyphase electrical system, a polyphase electrical circuit having portions to be operatively connected and disconnected, a switch for operatively connecting said portions, means for closing said switch, means for deriving a quantity dependent on the vector resultant of a positive phase sequence voltage component present on a first side of said switch and a positive phase sequence voltage component present on a second side of said switch, and means responsive only to said quantity for preventing closure of said switch. 7

2. In a polyphase electrical system, a polyphase electrical circuit having portions to be operatively connected and disconnected. a switch for operatively connecting said portions, means for closing said switch, control means responsive only to the vector resultant of positive phase sequence components on opposite sides of said switch for preventing closure of said switch, and means responsive to a predetermined condition of one of said portions of said polyphase electrical circuit for rendering said control means ineffective to prevent closure of said switch.

3. In a polyphas electrical system, a polyphase electrical circuit having portions to be operatively connected and disconnected, a separate source of polyphase electrical energy associated with each of said portions of said polyphase electrical circuit, a switch for operatively connecting said portions, means for tripping said switch, means for closing said switch, control means responsive only to the resultant of positive phase sequence components present in said polyphase electrical circuit on opposite sides of said switch for pre venting closure of said switch, and means responsive to a voltage condition of one of said portions of said polyphase electrical circuit for rendering said control mean ineffective to prevent closure of said switch.

4. In a polyphase electrical system, a polyphase distribution circuit, aplurality of sources of polyphase electrical energy for energizing said distribution circuit, and separate switch means for controlling the connection and disconnection of each of said sources of polyphase electrical energy to said distribution circuit; each of said switch means including a switch for connecting the associated source of polyphase electrical energy to said distribution circuit, means for tripping said switch, means for closing said switch, control means responsive only to the difference between positive phase sequence. components present in said polyphase electrical circuit on opposite sides of said switch for preventing closure of said switch, and means responsive to a voltage condition of said distribution circuit for rendering said control means ineffective to prevent a closure of said switch. I

5. In a polyphase electrical distribution circuit having portions to be operatively connected and disconnected, a switch for operatively connecting said portions, means for tripping said switch, means for closing said switch, and auxiliary means effective when phase conditions across the contacts of said switch are incorrect for preventing operation of said closing means, said auxiliary means comprising first means for deriving from a first one of said portions a quantity proportional to a positive phase sequence component therein, second means for deriving from a second one of said portions a quantity proportional to a positive phase sequence component therein, and means controlled only by the vector resultant of said quantities for preventing operation of said closing means.

6. In a polyphase electrical distribution circuit having portions to be operatively connected and disconnected, a switch for operatively connecting said portions, means for tripping said switch, means for closing said switch, and auxiliary means effective when phase conditions across the contacts of said switch are incorrect for pre* venting operation of said closing means, saidauxiliary means comprising a control relay having a single operating winding for preventing operation of said closing means, and means connecting said single operating winding to said portions for energization therefrom, said last named means including variable impedance means connected across the contacts of said switch and having an impedance value responsive to any incorrect phasing condition across the contacts of said switch for effecting an operation of said control relay in response to an incorrect phasing condition across the contacts of said switch.

'7. In a polyphase electrical distribution circuit having portions to be operatively connected and disconnected, a switch for opcratively connecting said portions, means for tripping said switch, means for closing said switch, and auxiliary means effective when phase conditions across the contacts of said switch are incorrect for preventing operation of' said closing means, said auxiliary means comprising a first positive phase sequence voltage filter associated with a first one of said portions, a second positive phase sequence voltage filter associated with a second one of said portions, and means responsive only to the vector difference between the output voltages of said'filters for preventing operation of said closing means.

8. In a polyphase electrical system, a polyphase distribution circuit, a plurality of sources of polyphase electrical energy for energizing said dis tribution circuit, and separate switch means for controlling the connection and disconnection of each of said sources of polyphase electrioal'energy relative to said distribution circuit; each of said switch means including a switch for connecting the associated source of polyphase electrical energy to said distribution circuit, means for trip ping said switch, means for closing said switch, and auxiliary means effective when phase condi tions across the contacts of said switch are incorrect for preventing operation of said closing means, said auxiliary means comprising a'first positive phase sequence voltage filter associated with a first one ofsaid portions, a second positive phase sequence voltage filter associated with a second one of said portions, a relay effective when energized from a single source of electrical energy for preventing operation of said closing means, and means for energizing said relay in accordance with the vector difference between the outputs of said filters.

9. In a polyphase electrical system, a polyphase distribution circuit, a plurality of sources of polyphase electricalen'ergy for energizing said distri bution circuit, and separate switch means for controlling the connection and disconnection of each of said sourcesof polyphase electrical ener'gy relative to said distribution circuit; each of said switch means including a switch for connecting the associated source of poiyphase electrical energy to said distribution circuit, means for tripping said switch, means for closing said switch, and auxiliary means efiective when phase conditions across the contacts ofsaid switch are incorrect for preventing operation of said closing means, said auxiliary means comprising a first positive phase sequence voltage filter associated with a first one of said portions, 9, second positive phase sequence voltage filter associated with a second one of said portions, a relay efiectiv'e' when energized from a single source of electrical ener y for preventing operation of said' closing means, means for energizing said relay in accordance with the difference between the outputs of said filters, and means responsive to a function of voltage present on said distribution circuit for rendering said relay ineffective to prevent opera tion of said closing means.

'JOHN S. PARSONS. 

